File 1450/1919 ‘Mesopotamia & Kurdistan: Geological Reports on’ [‎218r] (466/522)

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BBSttESOSSSSKBSi
•some of the sandstonos maj have occasionally projected in the form of low mounds. Near the
Lower Fars this deposit contains water-worn blocks of white gypsum. One occasionally gets an
impression of slight dip in the alluvium. The boundary mapped is purely arbitrary being the
approximate limit of Tertiary exposures.
The New Alluvium fringing the river calls for no remarks.
STRUCTURE.
As already stated the Hamrin and Makhul ranges coincide with a remarkably long and
persistent, simple anticline. A second anticline commences E. of the Humr Plain and continues
north-north-westwards in the Jabal-Chanuqah. The distance between the two anticlinal axes, which
are not quite parallel, varies from 3^ to 5| miles, the syncline between being occupied by the Red
Clay and Sandstone Series.
The Hamrin-Makhul anticline is slightly asymmetric, the S.W. limb being a little steeper than
the N.E. As the folding movement, in all probability, came from the N.R., being part of that
gigantic system of loops which constitute the Himalaya, the Afghan, Baluchistan and Persian
mountain systems, we thus remark a tendency for the fold to be pushed over towards the direction
of movement.
The details of the structure are as follows, commencing at the Mukhailah Pass and proceeding
north-westwards. The crest of the anticline sinks to a minimum close to and a little E. of this pass,
E.S.E. of which point it is seen rising gently on a very broad, open, round and regular fold. Across
the pass the anticline, omitting slight irregularities on the N.E. side, is practically symmetrical, while
the outcrop of the Lower Fars is reduced to about miles in width. W.N.W. of the pass the fold
rises very gradually, at first about 2°—3° but becoming less and less for some 2^ miles where it
reaches a maximum altitude. Beyond, the anticline pitches in an equally gradual and gentle fashion
for another 2 miles, after which it rises again gradually and steadily as far as the word “Jabal” on
the i ins. map, where for two or three miles no perceptible pitch is measurable ; at this crest-
maximum the Lower Fars outcrop is over 2| miles in width. It then slowly begins to sink, the pitch
gradually increasing to over 5° when a point is reached about a mile from the Tigris where it once
more rises very slightly, forming with a short distance of the outcrop on the west bank of the river,
a small dome area, which is slightly steeper on its S.W. aspect than elsewhere, and whose centre is
beautifully shewn in the river by concentric ellipses of limestone and gypsum bands, three of the
former seeping oil. Up the Jabal-Makhul the crest rises, distinctly at first, less and less perceptibly
afterwards. Persistent mist prevented my determining the crest-maxima in this range, but there
seems to be a long horizontal stretch immediately S. of Qalah Jabbar, and perhaps another maximum
S.S.W. of Mushak. Opposite Ain Dibs there is a distinct pitch of 5° to the N.N.W.
With regard to the flanks of the fold, the dip at Ain Nukhailah rises to 40° on each side.
Steeper dips occur locally immediately W.N.W., but where sections B—B has been drawn the
general maximum dip on the N.E. is about 35°, that on the S.W. between 35° and 40°. On the S.W.
flank, some 5 miles from Fathah a small subsidiary wrinkle makes its appearance and persists for
about 3 miles giving vertical and reversed dips along the Lower Fars boundary ; this is probably a
result of the pitch of the fold. This pitch is accompanied by a flattening of the arch which at Fathah
is very broad and gentle.
The Jabal-Makhul shows considerable asymmetry at first, dips of perhaps 25° (the maximum dip
is concealed beneath alluvium) on the N.E. being balanced by dips of 65°, 75° and 80 on the S.W.
Near Jabbar the asymmetry becomes less, 27° on the N.E., and 57° on the S.W. Across Ain Dibs
we have about 25° average maximum on the N.E. against 40° on the S.W., the latter flank steepening
rather suddenly towards the base of the range. Figures for Makhul must be accepted as approximate
only, the river on one side and the alluvium on the other marking the maximum dip. As a whole
the crest is broad and rounded in both ranges ; in longitudinal section it is also rounded.
The river has pierced the range at a weak spot where the crest has sunk to the small low dome
between the two crest-minima, and where the direction of the fold somewhat abruptly changes from
62° W. of N.—62° E. of S. to nearly due N.W.—S.E. ; dip-faulting may have assisted the river in
this. That this gap dated at least from Pleistocene times, is, I think, shown by the presence in its
neighbourhood of the conglomerate of that age.
PETROLEUM.
Natural Indications. Seepages of tarry oil and bitumen are too numerous on both river
banks around the opposite Fathah to be indicated on the map. Bitumen impregnating earth is to
be seen at various horizons, and has frequently been forced up vertical fissures. Three separate oil
horizons of seeping cellular limestone can be distinctly traced for some distance, passing from one
■side of the river to the other. u Gouttes” of dark oil are seen continually floating down the river,
and have been collected and utilised by the Sappers ; there is a strong odour of Hydrogen Sulphide
on both banks. The water trickling from the small streams into the river are milky with suspended
sulphur, and specks and patches of this mineral are locally common in the clays and gypsum ; a tarry
oil usually contaminates this water and there is then a confliction of the odours of hydrogen sulphide
and that of aromatic hydrocarbons. Similar indications were noticed in a stieam-comse 2-2 miles
E.S.E. of Fathah on the S. side of the range, and others about 5 miles above Fathah on the N.E.
side of the Jabal-Makhul ; these are merely instances and there are doubtless others. Their
particular abundance at the gap made by the river may be due to disturbance of the strata caused
by the twist in the anticline and the pitch of its axis. Seepages are frequently found wheie a fold
pitches, perhaps on account of disturbance in the beds.
Prospects of Boring. Mr. James divided the Lower Fars of the large Persian Oilfield into
three zones, n, b and c, ci being the oldest. The Hamrin beds seem to agiee veiy close!}- with his
b zone, and as the important oil horizons occur in the cellular limestones of the lowest oi a zone,
there is good reason to suppose that such limestones aie within easy access oi the diill, thiee at least
of these petroliferous limestones, which extend up into his middle oi b zone, aie evidently icpie-
.sented by the denuded seeping limestones on the rivet banks. The structure could scaicely be more